The invention concerns a pipette for transferring liquids which comprises at least one piston-cylinder arrangement arranged so that it can be provided with a transfer tip.
Pipettes of this type are generally known, an example being described in the U.S. Pat. No. 5,614,153. Such a pipette allows small quantities of a liquid to be transferred in a replaceable tip mounted to the free end of the pipette cylinder. This transfer occurs without pipette contamination, since the used tips are replaced by new tips. The pipette is equipped with a tip ejector that can be actuated manually and comprises an ejection mechanism sliding along the cylinder until it hits the tip and pushes it so that it will separate from the cylinder. In this pipette the ejection mechanism has an invariable stroke length, and its final position is fixed.
The tips that are used can come from different manufacturers or have different shapes, so that their dimensions can vary. Thus, the position of the tips on the cylinder can differ depending on the variants available on the market and on the force of fixation. This leads to differences in the position of the edge of the tip hit by the ejection mechanism. Since the differences in position are of the same order of magnitude as the stroke of the ejection mechanism, certain tips will not be ejected or may encounter the ejector before forming a close fit between the tip and the pipette cylinder.
It is one objective of the invention to realise a pipette that allows tips to be attached and ejected in a reliable manner, particularly while allowing for the variable position of the tip edge relative to the pipette. Such a pipette is preferably designed so that it is robust and easy to use.
The present liquid transfer pipette comprises at least one piston-cylinder arrangement in which the cylinder can be provided with a replaceable tip, a piston actuating device that induces the drawing up and discharging of the liquid, and a tip ejector device that comprises an ejection mechanism that can be displaced along the cylinder, its particular feature being that the ejector device comprises a device for position adjustment so arranged that the end position attained during a tip ejection operation by the end of the ejection mechanism at the end of a stroke can be modified. It should be noted that in practice, the adjustment will generally be made by adjusting the starting position of the free edge of the ejection mechanism that is intended to hit the upper edge of the tip. All embodiments of the present pipette allow tips of different shapes and dimensions to be attached and ejected in a reliable manner.
The position adjustment device may comprise a sleeve arranged on the cylinder of the piston-cylinder arrangement which cooperates with the ejection mechanism so as to allow the end position of the extremity of the ejection mechanism to be adjusted relative to the cylinder. The sleeve and the ejection mechanism can be coupled by threaded segments or by a catch or other element resting on a crown with sloping surface, in such a way that the position of the ejection mechanism is adjusted by a relative rotation between the sleeve and this mechanism. Thus, in a first embodiment the ejection mechanism can be rotated while the sleeve is held fixed, but in an alternative embodiment the sleeve can be rotated while the ejection mechanism is fixed. The sleeve and/or the ejection mechanism can be provided with notches, with a catch or similar elements defining their angular positions relative to the counterpart. Advantageously, the sleeve that can be mounted on a segment of the cylinder, and the ejection mechanism are readily accessible and adjustable.
In modifications of the position adjustment device a sleeve is used, for instance, the position of which can be adjusted relative to the ejection mechanism and which is mounted on this mechanism in such a way that it forms the ejecting extremity of this mechanism. The sleeve and the ejection mechanism can have corresponding threaded segments or comprise other means of attachment which allow the position of the sleeve to be adjusted as a function of the tip being used.
In another modification a position adjustment device is used where the end position of the ejection mechanism can be modified by a variation of the stroke of the ejection mechanism relative to the cylinder. The ejection mechanism can for instance be coupled to its actuating device via an organ of variable length so that at least an end position of the actuating mechanism can be modified.
Other aspects, objectives and advantages of the invention will become apparent from the following description, accompanying drawings, and the claims.